Magnetic-inductive flow meters are distinguished by very accurate measurement results, no pressure loss being caused in the piping system by the measurement. Moreover, magnetic-inductive flow meters have no components that move or project into the measuring tube and which, for example, would be subject to wear by measuring medium flowing past.
The measuring principle that is used in exemplary embodiments disclosed herein is based on Faraday's law of induction which states that a voltage is induced in a conductor moving in a magnetic field. When this law of nature is employed in metrology, the electrically conductive measuring medium flows through a measuring tube in which a magnetic field is generated perpendicular to the flow direction. The voltage induced in the measuring medium is tapped by an electrode arrangement. It is possible therefrom to determine the volume flow of the measuring medium—or by taking account of the density—the mass flow thereof, since the measurement voltage thus obtained is proportional to the mean flow rate of the flowing measuring medium.
A generic magnetic-inductive flow meter is known from DE 2004 053 065 A1. The flow meter substantially includes a measuring tube made from metal through which measuring medium flows and on which there is externally arranged a magnetic unit for generating a magnetic field perpendicular to a flow direction of the measuring medium. A pair of measuring electrodes penetrating the wall of the measuring tube in an opposed fashion is provided in the vicinity of the magnetic unit. The measuring medium flowing through the measuring tube is to be electrically insulated from the measuring tube which can consist of metal in order for the magnetic-inductive measuring principle to function. Since the measuring tube can be integrated in a pipeline, electrical grounding is carried out in this situation. In order to insulate the measuring tube electrically, the inside wall thereof is therefore coated with an elastic plastic. In many cases, a so-called liner is inserted into the measuring tube and forms a thin-walled elastic coating which can be resistant to corrosion by the measuring medium. The measuring tube is integrated in the further extent of the pipeline via double-sided flange sections.
The flow signal formed is measured at the electrodes in contact with measuring medium. Unipartite or multipartite electrodes for flow measuring devices are known to this end. It is possible to use appropriate materials as regards a desired suitability for abrasive media, as well.
DE 196 53 184 A1 discloses a signal processing circuit for such a flow measuring device which reveals a position of the magnetic and electrical electrodes.
It is known from DE 10 2007 032 879 A1 to guide electrical connecting lines between electrodes, and to guide means for processing measured values through a common leadthrough in a lining of the measuring tube, and by a shortest route, to the electrodes. With such an arrangement, an area is defined which is limited approximately in a shape of a semicircle by the geometric connecting line between the oppositely situated electrical electrodes and the connecting lines leading to the electrodes. An external magnetic field can induce over the area an interference voltage which can distort the measurement voltage.